1. Field of the Invention
This invention relates to the manufacture of glass fiber mats by the wet-laid process and, more particularly, it is concerned with a method of improving the tensile strength of such mats upon being subjected to severe wet conditions.
2. Description of the Prior Art
Glass fiber mats are composed of glass fibers held together by a binder material. Typical binders used in the industry are urea-formaldehyde resins, phenolic resins, bone glue, polyvinyl alcohols, and latexes. These binder materials are impregnated directly into the fibrous mat and set or cured to provide the desired integrity for the glass fibers. The most widely used binder is urea-formaldehyde because it is inexpensive. Unfortunately, urea-formaldehyde binder is deficient in one or more respects for glass fiber mats. In particular, the tensile strengths of mats bound with urea-formaldehyde deteriorate appreciably when the mats are subjected to wet conditions, which are normally encountered in their use in roofing products. Such roofs may fail if their wet tensile strength is much lower than its dry tensile strength.
Accordingly, it is an object of this invention to provide glass fiber mat roofing shingles and built-up roofing products which retain a substantial portion of their dry tensile strength even under severe wet conditions.